1. Field of the Invention
This invention relates to an ignition timing control system for an internal combustion engine, more particularly to an ignition timing control system for an internal combustion engine in which engine warm-up under cold starting is facilitated or improved.
2. Description of the Related Art
When starting an internal combustion engine, the ignition timing is conventionally retarded from the MBT (Minimum Spark advance for Best Torque) so as to facilitate or improve engine warm-up. Specifically, since the engine output drops by retarding the ignition timing from the MBT, the vehicle operator opens the throttle valve to increase the amount of fuel supply. This raises the engine coolant temperature.
On the contrary, Japanese Patent Publication No. Hei 5 (1993) 69,991 teaches advancing the ignition timing towards the MBT from a warm-up ignition timing, when the engine temperature is quite low, so as to prevent the engine output from dropping excessively. Since the combustion speed is slower at low engine coolant temperatures, this prior art proposes to advance the ignition timing towards the MBT to avoid excessive engine output decrease.
The engine coolant temperature is not always quite as low as is expected by the prior art (Hei 5 (1993)-69,901). Generally speaking, however, the engine coolant temperature at engine starting is relatively low and the combustion is slow. Accordingly, if the ignition timing is retarded at engine starting, as taught by the conventional technique, the combustion is further delayed and is apt to be degraded. For that reason, it is difficult in the conventional technique to retard the ignition timing to a sufficient extent, requiring the engine warm-up to be better facilitated or improved.
Moreover, when the ignition timing is retarded, the gas temperature drops during the combustion stroke, but rises at the expansion stroke and the exhaust stroke (which are partially overlapped with the expansion stroke). In the case that, due to spatial limitation or some similar factors, the engine does not have a sufficient engine coolant passage around the exhaust, the engine can not utilize the gas temperature rise during the expansion stroke and the exhaust stroke, in particular the exhaust stroke to a full extent. Rather, the engine is significantly affected by the lower temperature during the combustion stroke, resulting in a decrease in the quantity of heat supplied to the engine coolant.
Thus, the conventional technique is disadvantageous in that the engine can not utilize, to a full extent, the engine warming effect obtained by increasing the amount of fuel supply.
An object of the present invention is therefore to overcome the drawbacks explained in the foregoing by providing an ignition timing control system for an internal combustion engine which facilitates or improves warm-up at engine starting, even when the engine does not have a sufficient engine coolant passage around the exhaust port due to spatial limitation.
This invention achieves these objects by providing a system for controlling an ignition timing of an internal combustion engine, including: engine operating condition detecting means for detecting operating conditions of the engine including at least an engine speed, an engine load and an engine coolant temperature; basic ignition timing determining means for determining a basic ignition timing from mapped data prepared based on MBT using the detected engine speed and the engine load; output ignition timing determining means for determining an output ignition timing based at least on the determined basic ignition timing; and ignition means for igniting an air-fuel mixture in a cylinder of the engine; wherein the system includes:advancing correction amount determining means for determining an ignition timing advancing correction amount based on at least the detected engine coolant temperature; and engine cold start determining means for determining whether the engine is under a predetermined cold starting condition based on the detected operating conditions of the engine;